To support transmission at a peak data rate of up to 1 Gbit/s in a communications system, a Long Term Evolution (LTE) system now uses a CA manner as a method of extending LTE bandwidths. Primarily, the CA manner is to aggregate multiple component carriers (CC) into a carrier of a larger bandwidth to support high-rate data transmission. FIG. 1 is a schematic structural diagram of bandwidths used for transmitting data with a CA technique. As shown in FIG. 1, a downlink channel bandwidth used for transmitting data is a result of aggregating five 20 M carriers including carrier 1, carrier 2, carrier 3, carrier 4, and carrier 5.
CA comes in two types, namely, intra-band carrier aggregation (intra-band CA) and inter-band carrier aggregation (inter-band CA). For intra-band CA, because multiple aggregated carriers are in the same band, their data transmission coverage keeps consistent. For the inter-band CA, because the multiple aggregated carriers are in different bands, when frequencies in a band are far from frequencies of another band, the data transmission coverage varies sharply between the carriers. Generally, carriers in a low band have large coverage, and carriers in a high band have small coverage. As shown in FIG. 2, FIG. 2 is a schematic diagram of coverage of different carriers under inter-band CA in the prior art, a blank region is coverage of an 800 Mhz carrier, and a filled region is coverage of a 3 Ghz carrier. Evidently, the coverage of the 3 Ghz carrier is smaller than the coverage of the 800 Mhz carrier.
As shown in FIG. 2, if a user equipment (UE, User Equipment) is located in a central region of a cell, the UE may use both high-band carriers and low-band carriers in the inter-band CA to transmit data. However, when the UE moves to an edge of the cell, the UE is unable to use high-band carriers for transmitting data. The UE at the edge of the cell has much lower throughput of data transmission than the UE at the center of the cell.
Therefore, to increase the data transmission throughput of the UE at the edge of the cell and expand coverage of the high-band carriers, a relay node (RN, relay Node) or a small base station such as a pico base station or a Home eNB may be used on a network side of the cell to expand the coverage of the high-band carriers. As shown in FIG. 3, which is a schematic structural diagram of expanding coverage of high-band carriers in the prior art, two RNs are added to expand the coverage of the high-band carriers, so as to expand the coverage of the high-band carriers. However, even if the RNs are applied to expand the coverage of the high-band carriers, the UE at the edge of the cell still needs to aggregate carriers from two different sites in order to use both component carriers in the high band and component carriers in the low band. That is, the carriers in the low band come from a macro base station (DeNB, Donor eNodeB), and the carriers in the high band come from the RN or another small base station, which is called inter-site carrier aggregation (inter-site CA) herein.
Therefore, how a UE can aggregate the data transmitted over carriers in different bands of the DeNB and the RN, and improve data transmission throughput of the UE, is an urgent issue to be resolved.